The number of properties infected with myrtle rust nationally has risen to 25, the Ministry for Primary Industries says.

These properties include a mix of plant nurseries, private gardens, retailers, distributors and one orchard.

A bulk of the affected properties are in Taranaki on 20, with three in Northland and two in Waikato.

MPI said the rust has not yet been found on feijoa.

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"To date, the rust has been found on seedlings of pohutukawa, Lophomyrtus bullata [ramarama], eucalyptus, manuka and Syzygium smithii," the ministry said.

A very established pohutukawa hedge belt in Taranaki was one of the most recent detections of extensive infection.

The first identified infected property in Northland (Kerikeri Plant Production) has been cleared to reopen following the destruction and safe removal of all affected plants and treatment with fungicide.

Plants from this nursery are safe for sale and distribution, the ministry said.

The Big Jims retail outlet in Taranaki will also reopen on Wednesday following treatment.

The ministry earlier said it had received unprecedented support from the public, with more than 450 reports of suspected symptoms.

People are being encouraged to look for signs of myrtle rust, a fungal plant disease that was first found at a Kerikeri nursery in early May.

Myrtle rust can cause serious damage to manuka trees, which is used for honey production and also attacks native trees, such as pohutukawa and rata.

Besides applying fungicide in small areas, there is no other known method for controlling it in the wild.